1. Field of the Invention
The present invention relates to a resolver for detecting a rotational position, and more particularly, to a flat resolver having a transformer winding.
2. Description of the Related Art
A related art resolver having a transformer winding for supply of a power source is illustrated in FIG. 7.
FIG. 7 is a partially cross-sectional view of a related art resolver having a cylindrical stator assembly and a rotor assembly which is disposed coaxially with the cylindrical stator assembly.
In FIG. 7, a resolver 100 has a cylindrical stator assembly 101, a rotor assembly 102 disposed coaxially with the stator assembly 101, and a transformer portion 103 including an inner core 104 and an outer core 105 disposed coaxially with the inner core 104.
A stator portion includes the outer core 105 and the stator assembly 101, which are axially installed in a cylindrical housing 106.
A rotor portion includes the inner core 104 and the rotor assembly 102, which are axially installed around a shaft 107.
A winding of the inner core 104 of the transformer portion 103 is connected via a crossover wire to a rotor winding of the rotor assembly 102. The winding portions of the resolver are coaxially arranged. Therefore, in order to prevent the axis from being deviated from a center, two bearings 108 are axially arranged with a spacing.
In the example of FIG. 7, the inner core 104, the rotor assembly 102 and the two bearings 108 are axially disposed end to end. Therefore, the resolver has a large length in the axial direction. Therefore, the configuration of the stator assembly 101 and the rotor assembly 102, which are cylindrically arranged, and the configuration of the inner core portion and the outer core portion, which are cylindrically arranged, are complicated, so that the whole structure cannot be miniaturized.
To reduce the length in the axial direction, a disk-like resolver or a flat resolver has been proposed (see, for example, JP-A-08-136211 and JP-A-05-010779).
FIG. 8 is a cross-sectional view illustrating a related art flat resolver disclosed in JP-A-08-136211.
In FIG. 8, a stator portion has a stator core 111 and a stator sheet coil 113.
The stator core 111 includes a disk-like magnetic plate 112 of a material having good high frequency-core loss characteristics (e.g., ferrite, etc.).
The stator sheet coil 113 is fixed to a side surface of the magnetic plate 112 using an adhesive or the like. The stator sheet coil 113 is formed as follows. A primary winding 114 of a rotary transformer portion A and a detection winding 115 of a signal generation portion B are formed of a plate-like conductive material using a printed wiring technique, such as etching, printing or presswork. The primary winding 114 and the detection winding 115 are attached on top and bottom surfaces of a disk-like insulating substrate of polyimide. Further, the surface of the conductor material is subjected to an insulating treatment using polyimide resin or the like.
A rotator portion has a rotator core 116 and a rotator sheet coil 118. The rotator portion is fixed to a shaft 119. The rotator core 116 is in the shape of a disk and is opposed to the stator core 111 with a spacing therebetween. The rotator core 116 includes a magnetic plate 117 as does the stator core 111.
The rotator core 116 has a center portion which is fixed to a shaft 119, and therefore, is supported via a bearing 121 by a bracket 120 which is fixed to the stator core 111.
The rotator sheet coil 118 is fixed to a side of the magnetic plate 117 using an adhesive or the like. The rotator sheet coil 118 is formed as follows. A secondary winding 122 of the rotary transformer portion A and an excitation winding 123 of the signal generation portion B are similarly formed using the printed wiring technique. The secondary winding 122 and the excitation winding 123 are attached on top and bottom surfaces of a disk-like insulating substrate of polyimide. Further, the surface of the conductor material is subjected to an insulating treatment using polyimide resin or the like. Note that, when an adhesive is used to fix the stator core 111 and the rotator core 116 to the stator sheet coil 113 and the rotator sheet coil 118, respectively, the adhesive has a thickness of about 25 μm. Therefore, a magnetic gap is increased, leading to an increase in the power consumption. By adding soft magnetic powder (e.g., soft ferrite, etc.) to the adhesive, the relative permeability of the adhesive can be improved, so that the magnetic gap is reduced, leading to a decrease in the power consumption.
The related art flat resolver of FIG. 8 has the following problems.
(1) When the stator core 111 and the rotator core 116 are fixed to the stator sheet coil 113 and the rotator sheet coil 118, respectively, using an adhesive, the adhesive has a thickness of about 25 μm. Therefore, the stator sheet coil 113 may be mounted onto a surface of the stator core 111 with a tilt due to the thick adhesive layer or the rotator sheet coil 118 may be mounted onto a surface of the rotator core 116 with a tilt due to the thick adhesive layer. In this case, a gap between the stator and the rotator is not uniform, so that magnetic coupling between the stator and the rotator is distorted due to the tilt.
(2) The surface of the conductive material is subjected to the insulating treatment using polyimide resin or the like. Therefore, the gap between the stator and the rotator is not uniform due to the thickness of the resin layer on the conductive material, and the length in the axial direction between the stator and the rotator is increased. Therefore, magnetic coupling between the stator and the rotator is deteriorated.
(3) The primary winding 114 of the rotary transformer portion A and the detection winding 115 of the signal generation portion B are supported on the magnetic plate 112. The secondary winding 122 of the rotary transformer portion A and the excitation winding 123 of the signal generation portion B are supported on the magnetic plate 117. Only the magnetic plates 112 and 117 of the opposite sides form a magnetic path. The magnetic path is insufficient for formation of a magnetic flux effectively linking to the secondary winding 122 and the detection winding 115, so that leakage flux is significant.
The winding is formed of a plate-like conductive material using a printed wiring technique, such as etching, printing or presswork. Therefore, the number of turns in the winding cannot be large. It is difficult to obtain a large magnetic flux generated in the winding.